VISCOELASTICITY OF RUBBER-TOUGHENED POLY(METHYL METHACRYLATE) .1. DEFORMATIONAL BEHAVIOR

Viscoelasticity of a rubber toughened poly(methyl methacrylate) has be rn investigated bell in the linear and the non-linear range by means o f tensile creep and tensile constant strain rate tests. An empirical t ime-temperature-strain reduction scheme is proposed Lo analyze tile mo dulus data obtained at different temperatures and strain levels: a sin gle master curve and relevant lime-temperature and time-strain shift f actors have been obtained. Two different thermal histories were consid ered for testing. It lias been shown that, once aging effects can be c onsidered under conditions where aging time elapsed before testing is the same, modulus master curves obtained from linear and from non-line ar data substantially coincide. This shows that both temperature and s train level determine the modulus master curve ria their influence on a single variable: the free volume of the material.